Why should I not use HTML frames?
See the question and my original answer on StackOverflowOne good reason to avoid frames today is they have been deprecated in HTML 5: Chapter 11 Obsolete features
11.2 Non-conforming features
Elements in the following list are entirely obsolete, and must not be used by authors:
[...]
frame
frameset
noframes
Either use iframe and CSS instead, or use server-side includes to generate complete pages with the various invariant parts merged in.